1. Field of the Invention
This invention relates to novel surfactant compositions and methods of using the same to enhance the recovery of oil from subterranean formations. More particularly, this invention comprises injecting novel combinations of anionic surfactants and hydrotropes with steam into oil-bearing formations to greatly increase heavy oil recovery as compared with the use of steam alone.
2. Description of the Prior Art
The use of secondary and tertiary oil recovery techniques, with or without the addition of various reagents such as surfactants, water thickeners and the like to recover crude oil left behind in formations after the "primary" oil has been withdrawn is well established in the art. These displacement methods have been improved by the addition of surfactant compositions in both secondary and tertiary processes, for example where a formation has already been waterflooded at least once.
Representative of these prior art compositions and methods are those taught in U.S. Pat. Nos. 3,348,611 to Reisburg; 3,885,626 to Gale et al; 3,901,317, to Plummer et al; 3,994,342 to Healy et al; and 4,295,980 to Motz, all of which teach aqueous flooding techniques with at least one surfactant, and in some cases, with viscosity modifiers, co-surfactants or the like. In an unrelated field, U.S. Pat. No. 3,501,409 teaches a liquid washing detergent composition comprising said detergent in combination with a hydrotrope.. Similarly, U.S. Pat. No. 4,165,294 teaches a commercial photoresist stripping solution comprising an alkyl aryl sulfonic acid and a hydrotrope aromatic sulfonic acid. This composition, used to remove organic coatings from inorganic subtrates, is further characterized in requiring the presence of a solvent, and also requiring that the composition must be phenol-free and halogen-free. Finally, U.S. Pat. No. 3,354,091 discloses a heavy-duty liquid detergent consisting essentially of a 5-component composition requiring the presence of an alkali metal anionic surfactant, a polyphosphate salt, a hydrotrope, carboxymethylcellulose, and hydrogenated castor oil. Optionally, small amounts of sodium silicate may, for undisclosed reasons, be added as long as it does not adversely affect the desired results of the composition.
In addition to the aforedescribed aqueous flooding techniques, the art has also employed steam for tertiary oil recovery, utilizing the effect of heat to obtain heavy oil from the formations in which it is found. See, for example, U.S. Pat. Nos. 3,357,487 and 3,994,345. However, the mechanism and effects of surfactants under these high temperatures and diverse formation conditions remain unclear, and thus make it impossible to predict from a knowledge of the effects of aqueous surfactant systems which surfactants, if any, can advantageously be employed in these steam recovery conditions. This is even more true in the choice of any modifiers which might enhance the effectiveness of the surfactant.
It is, therefore, an object of this invention to provide a novel surfactant composition useful for enhancing steam recovery processes for tertiary recovery of heavy oil from subterranean formations, as compared with the use of steam alone.
It is a further object of this invention to provide an improved steam recovery process for enhanced oil recovery, utilizing the novel compositions provided herein.
Further objects and advantages of the compositions and methods of the present invention will become apparent in the course of the following detailed description thereof.